halkyon_app: instances, sign-in and sync plumbing for Halkyon's apps

What every Halkyon app's shell needs, taken from Halkyon Learn's and set
on halkyon_base's client: the instances a device keeps an account on,
the first start's tiles and where an instance keeps people's data, the
account switcher; signing in anonymously, with GitHub or an email code,
switching person and the start screen; the gates that build an app's
dependencies per instance and per person; and the sync service with its
status, Settings card and banner. Texts of its own in English and
German take the app's name; what only the app can say, it passes in.
Fakes for apps' tests are in testing.dart.

An instance's basics now name the app it serves (`app`, set by the
host's configuration), and an app accepts only an instance of its own.
SerialQueue and CoalescingRunner move into halkyon_core.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

packages/halkyon_app/test/sync/widget/sync_widgets_test.dart

@@ -0,0 +1,171 @@
+import 'package:flutter_bloc/flutter_bloc.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:halkyon_app/halkyon_app.dart';
+import 'package:halkyon_app/testing.dart';
+import 'package:material_ui/material_ui.dart';
+
+/// Where an app puts the sync's widgets: a banner on its home, a dot on its
+/// way to Settings, and the Sync card in Settings, which More leads to.
+class const _Home() extends StatelessWidget {
+  @override
+  Widget build(BuildContext context) => Scaffold(
+    body: Column(
+      children: [
+        AppMismatchBanner(onMore: () => _openSettings(context)),
+        SyncTroubleBadge(
+          child: IconButton(
+            tooltip: 'Settings',
+            icon: const Icon(Icons.settings),
+            onPressed: () => _openSettings(context),
+          ),
+        ),
+      ],
+    ),
+  );
+
+  static void _openSettings(BuildContext context) => Navigator.of(context).push(
+    MaterialPageRoute<void>(
+      builder: (context) => Scaffold(
+        appBar: AppBar(title: const Text('Settings')),
+        body: const SingleChildScrollView(child: SyncStatusCard()),
+      ),
+    ),
+  );
+}
+
+void main() {
+  /// What the next sync does: null goes through, anything else is thrown.
+  late Object? nextSync;
+
+  /// Shows the app on test.example.org once a first sync ran, with
+  /// [pending] changes kept from before that haven't reached the server.
+  /// (The service isn't started: its timers would outlive the test.)
+  Future<void> showApp(WidgetTester tester, {int pending = 0}) async {
+    final sync = SyncService(
+      ({required onMerge}) => switch (nextSync) {
+        final Object error => Future<void>.error(error),
+        null => Future<void>.value(),
+      },
+      pendingChanges: MemoryPendingChangesStore(pending),
+    )..syncNow();
+    addTearDown(sync.dispose);
+    await tester.pumpWidget(
+      BlocProvider(
+        create: (context) =>
+            SyncStatusBloc(sync)..add(const SyncStatusEventStarted()),
+        child: testApp(const _Home(), dependencies: TestAppDependencies()),
+      ),
+    );
+    await tester.pumpAndSettle();
+  }
+
+  Finder trouble() => find.bySemanticsLabel(RegExp('Sync needs attention'));
+
+  Future<void> openSettings(WidgetTester tester) async {
+    await tester.tap(find.byTooltip('Settings'));
+    await tester.pumpAndSettle();
+  }
+
+  setUp(() => nextSync = null);
+
+  testWidgets('shows nothing while sync goes through', (tester) async {
+    await showApp(tester);
+
+    expect(trouble(), findsNothing);
+    expect(find.byType(MaterialBanner), findsNothing);
+  });
+
+  testWidgets('a failed sync puts a dot on the way to Settings, and the '
+      'Sync card says what is wrong', (tester) async {
+    nextSync = Exception('No connection');
+    await showApp(tester);
+
+    expect(trouble(), findsOneWidget);
+    await openSettings(tester);
+    expect(find.text('Sync is failing'), findsOneWidget);
+    expect(find.textContaining('Last attempt failed at'), findsOneWidget);
+    expect(
+      find.text('No sync has completed since the app started'),
+      findsOneWidget,
+    );
+  });
+
+  testWidgets('the Sync card counts the changes that wait to sync, until a '
+      'sync takes them', (tester) async {
+    nextSync = Exception('No connection');
+    await showApp(tester, pending: 2);
+    await openSettings(tester);
+
+    expect(find.text('Sync is failing'), findsOneWidget);
+    expect(find.text('2 changes wait to sync'), findsOneWidget);
+
+    nextSync = null;
+    await tester.tap(find.text('Sync now'));
+    await tester.pumpAndSettle();
+    expect(find.text('Everything synced'), findsOneWidget);
+    expect(find.textContaining('wait to sync'), findsNothing);
+  });
+
+  testWidgets('Sync now syncs, and the trouble goes once a sync went '
+      'through', (tester) async {
+    nextSync = Exception('No connection');
+    await showApp(tester);
+    await openSettings(tester);
+
+    nextSync = null;
+    await tester.tap(find.text('Sync now'));
+    await tester.pumpAndSettle();
+
+    expect(find.text('Everything synced'), findsOneWidget);
+    expect(find.textContaining('Last completed at'), findsOneWidget);
+    await tester.pageBack();
+    await tester.pumpAndSettle();
+    expect(trouble(), findsNothing);
+  });
+
+  testWidgets("when the app and the server don't match, the banner says so "
+      'and More leads to the Sync card, until a sync goes through', (
+    tester,
+  ) async {
+    nextSync = const AppServerMismatchException();
+    await showApp(tester);
+
+    const banner =
+        "This app can't sync with test.example.org any more. Update it to "
+        'keep syncing.';
+    expect(find.text(banner), findsOneWidget);
+
+    await tester.tap(
+      find.descendant(
+        of: find.byType(MaterialBanner),
+        matching: find.text('More'),
+      ),
+    );
+    await tester.pumpAndSettle();
+    expect(
+      find.text("This app can't sync with test.example.org"),
+      findsOneWidget,
+    );
+    expect(
+      find.text(
+        'Update the app. If it is up to date, the server needs an update. '
+        'What you do meanwhile stays on this device and syncs afterwards.',
+      ),
+      findsOneWidget,
+    );
+
+    nextSync = null;
+    await tester.tap(find.text('Sync now'));
+    await tester.pumpAndSettle();
+    await tester.pageBack();
+    await tester.pumpAndSettle();
+    expect(find.text(banner), findsNothing);
+  });
+
+  testWidgets('an ordinary failure shows no banner', (tester) async {
+    nextSync = Exception('No connection');
+    await showApp(tester);
+
+    expect(find.textContaining('Update it to keep syncing'), findsNothing);
+  });
+}